I installed frame slider and I dropped my R6 last week but there were just minor scratches on Muffler(stock) and right mirror. No scratches on cowls(plastics). It's worth to buy it. I just got it from local yamaha dealership.
Even with frame slider you might get a crack on your cowls but when you drop it just hold it as much as you can like you are putting down on the ground slightly. (If you can) Just don't let it slam down that's how much you can reduce the damage.
If the ground is flat then you won't get a scratch on your cowls.